linux-kernel - Re: [PATCH v3 17/19] mm: memcg/slab: use a single set of kmem

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Date:   Tue, 26 May 2020 16:55:05 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Roman Gushchin <guro@...com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>, linux-mm@...ck.org,
        kernel-team@...com, linux-kernel@...r.kernel.org,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Mel Gorman <mgorman@...hsingularity.net>
Subject: Re: [PATCH v3 17/19] mm: memcg/slab: use a single set of kmem_caches
 for all allocations

On 4/22/20 10:47 PM, Roman Gushchin wrote:
> Instead of having two sets of kmem_caches: one for system-wide and
> non-accounted allocations and the second one shared by all accounted
> allocations, we can use just one.
> 
> The idea is simple: space for obj_cgroup metadata can be allocated
> on demand and filled only for accounted allocations.
> 
> It allows to remove a bunch of code which is required to handle
> kmem_cache clones for accounted allocations. There is no more need
> to create them, accumulate statistics, propagate attributes, etc.
> It's a quite significant simplification.
> 
> Also, because the total number of slab_caches is reduced almost twice
> (not all kmem_caches have a memcg clone), some additional memory
> savings are expected. On my devvm it additionally saves about 3.5%
> of slab memory.
> 
> Suggested-by: Johannes Weiner <hannes@...xchg.org>
> Signed-off-by: Roman Gushchin <guro@...com>

Reviewed-by: Vlastimil Babka <vbabka@...e.cz>

However, as this series will affect slab fastpaths, and perhaps especially this
patch will affect even non-kmemcg allocations being freed, I'm CCing Jesper and
Mel for awareness as they AFAIK did work on network stack memory management
performance, and perhaps some benchmarks are in order...